Field of the Invention
The present invention relates to a fuel cell stack formed by stacking a plurality of fuel cells each having an electrolyte electrode assembly. The electrolyte electrode assembly includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode.
Description of the Related Art
In general, a solid oxide fuel cell (SOFC) employs a solid electrolyte of ion-conductive oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly, for example, a membrane electrode assembly (MEA). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, generally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
In the fuel cell stack, in order to obtain the output voltage efficiently, the fuel cells need to be stacked together in a desired pressurized state. Further, in order to prevent leakage of a reactant gases such as a fuel gas and air as much as possible, it is required to apply pressure to the fuel cell stack in the stacking direction to seal reactant gas manifolds reliably.
To this end, an electrochemical cell stack disclosed in Japanese Laid-Open Patent Publication No. 2009-500525 (PCT) (hereinafter referred to as conventional technique 1) is known. As shown in FIG. 8, this electrochemical cell stack includes an electrochemical cell (proton exchange membrane (PEM) cell) stack 1a interposed between a first electrically conductive end plate 2a and a second electrically conductive end plate 3a. 
An end plate 4a is provided outside the second electrically conductive end plate 3a, and the end plate 4a and the first electrically conductive end plates 2a are connected by a plurality of walls 5a. An electrically insulating elastic pad 6a made of silicone or elastic polymer material is interposed between the second electrically conductive end plate 3a and the end plate 4a. According to the disclosure, in operation, the electrically insulating elastic pad 6a can compensate heat expansion or heat contraction of the electrochemical cell stack 1a. 
Further, in a flat plate type solid electrolyte fuel cell disclosed in Japanese Laid-Open Patent Publication No. 10-172594 (hereinafter referred to as the conventional technique 2), a separator 1b as shown in FIG. 9 is provided, and a plurality of unit cells (not shown) and separators 1b are stacked alternately. Each of the unit cells includes a solid electrolyte layer and an air electrode and a fuel electrode provided on both surfaces of the solid electrolyte layer. A gas supply hole 2b and a gas discharge hole 3b are formed at a pair of diagonal positions of the separator 1b, and a plurality of gas flow grooves 4b are formed at the central part of the separator 1b. 
A gas throttle section 5b and blocks 6b are provided between the gas supply hole 2b and the inlet of the gas flow grooves 4b. According to the disclosure, in the structure, the pressure loss of the gas discharged from the gas supply hole 2b is increased, and it becomes possible to distribute the gas uniformly.